Field of the Invention
The present invention relates to an electrical cable, and applies typically, but not exclusively, to the electrical cables used in aeronautics, for example on board aeroplanes.
Description of the Related Art
This type of electrical cable must satisfy numerous criteria necessary for its use in aeronautics, especially when it is subjected to high voltages, of the order of 230 V, and for cables located in the non-pressurized areas.
This relatively high voltage, combined with aeronautical constraints, such as humidity, high temperature and low pressure, may give rise to partial discharges (PD) on electronic equipment, such as electrical cables. Now, partial discharges, which are minute electric arcs in the material insulating the cable, bring about over time degradation of the insulating material, which can lead to rupture of the dielectric.
Other criteria may also be taken into consideration, for instance the weight and diameter of said cable, which must not be excessive, and the markability of said cable in order to enable its identification, when necessary.
In the prior art, it is known practice to equip aeroplanes with hook-up wires, these wires comprising: a conductive element surrounded by a first layer made of polyimide from 0.017 to 0.065 mm thick, which is itself surrounded with a layer made of polytetrafluoroethylene PTFE from 0.1 to 0.22 mm thick for nominal conductive cross sections ranging from 0.15 to 95 mm2. However, for such hook-up wires, the applied voltage is of the order of 115 V.
Document EP 1 498 909 concerns a multilayer composition whose function is to insulate and/or protect electrical conductive materials, such as cables for aeronautics. This insulating composition successively comprises around the electrical element to be protected a first layer made of polyimide (PI), a second layer made of perfluoro(alkyl vinyl ether)/tetrafluoroethylene copolymer (PFA) and optionally an outer layer made of polytetrafluoroethylene (PTFE). The thickness of the PI layer ranges from 8 to 150 μm and the thickness of the PTFE ranges from 1 to 200 μm. However, the resistance to partial discharges of a cable surrounded with this composition is not optimized for high voltages either, such as 230 V.